Why was the union defeated at Chancellorsville?

The Union was defeated at Chancellorsville primarily due to General Robert E. Lee's bold and risky tactics, including his decision to divide his forces in the face of a larger Union army. This maneuver allowed Confederate troops under General Stonewall Jackson to launch a surprise attack on the Union flank, leading to significant confusion and disarray among Union ranks. Additionally, poor communication and coordination among Union commanders hindered their response to the Confederate assault, ultimately contributing to their defeat in this pivotal battle.